Hi,  If you need rubber cement or rubber cement thinner in the USA,
you can get it easily from Dick Blick Art Supply.  The URL is

  http://www.dickblick.com/

Also, you should check the MMD Archives on this subject.  Some
interesting things happen to sealed pouches over time depending on
which sealer you use.  You should be especially careful not to leave
the chest out of the piano for a long time while you work on it because
UV light tends to deteriorate some of the sealers commonly used.

By the way, I think the Evo-Stik material that Nicholas Simons
mentioned today is called Plio-Bond in the US.  It's thinned with
acetone as he said.  I've used it to seal both leather and bellows
cloth with much success.  It even has an UV inhibitor in it.

Regards,
Craig Smith